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  <div class="section" id="module-codecs">
<span id="codecs-codec-registry-and-base-classes"></span><h1><a class="reference internal" href="#module-codecs" title="codecs: Encode and decode data and streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">codecs</span></code></a> --- Codec registry and base classes<a class="headerlink" href="#module-codecs" title="永久链接至标题">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.7/Lib/codecs.py">Lib/codecs.py</a></p>
<hr class="docutils" id="index-0" />
<p>This module defines base classes for standard Python codecs (encoders and
decoders) and provides access to the internal Python codec registry, which
manages the codec and error handling lookup process. Most standard codecs
are <a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encodings</span></a>, which encode text to bytes,
but there are also codecs provided that encode text to text, and bytes to
bytes. Custom codecs may encode and decode between arbitrary types, but some
module features are restricted to use specifically with
<a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encodings</span></a>, or with codecs that encode to
<a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a>.</p>
<p>The module defines the following functions for encoding and decoding with
any codec:</p>
<dl class="function">
<dt id="codecs.encode">
<code class="descclassname">codecs.</code><code class="descname">encode</code><span class="sig-paren">(</span><em>obj</em>, <em>encoding='utf-8'</em>, <em>errors='strict'</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.encode" title="永久链接至目标">¶</a></dt>
<dd><p>Encodes <em>obj</em> using the codec registered for <em>encoding</em>.</p>
<p><em>Errors</em> may be given to set the desired error handling scheme. The
default error handler is <code class="docutils literal notranslate"><span class="pre">'strict'</span></code> meaning that encoding errors raise
<a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> (or a more codec specific subclass, such as
<a class="reference internal" href="exceptions.html#UnicodeEncodeError" title="UnicodeEncodeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnicodeEncodeError</span></code></a>). Refer to <a class="reference internal" href="#codec-base-classes"><span class="std std-ref">Codec Base Classes</span></a> for more
information on codec error handling.</p>
</dd></dl>

<dl class="function">
<dt id="codecs.decode">
<code class="descclassname">codecs.</code><code class="descname">decode</code><span class="sig-paren">(</span><em>obj</em>, <em>encoding='utf-8'</em>, <em>errors='strict'</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.decode" title="永久链接至目标">¶</a></dt>
<dd><p>Decodes <em>obj</em> using the codec registered for <em>encoding</em>.</p>
<p><em>Errors</em> may be given to set the desired error handling scheme. The
default error handler is <code class="docutils literal notranslate"><span class="pre">'strict'</span></code> meaning that decoding errors raise
<a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> (or a more codec specific subclass, such as
<a class="reference internal" href="exceptions.html#UnicodeDecodeError" title="UnicodeDecodeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnicodeDecodeError</span></code></a>). Refer to <a class="reference internal" href="#codec-base-classes"><span class="std std-ref">Codec Base Classes</span></a> for more
information on codec error handling.</p>
</dd></dl>

<p>The full details for each codec can also be looked up directly:</p>
<dl class="function">
<dt id="codecs.lookup">
<code class="descclassname">codecs.</code><code class="descname">lookup</code><span class="sig-paren">(</span><em>encoding</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.lookup" title="永久链接至目标">¶</a></dt>
<dd><p>Looks up the codec info in the Python codec registry and returns a
<a class="reference internal" href="#codecs.CodecInfo" title="codecs.CodecInfo"><code class="xref py py-class docutils literal notranslate"><span class="pre">CodecInfo</span></code></a> object as defined below.</p>
<p>Encodings are first looked up in the registry's cache. If not found, the list of
registered search functions is scanned. If no <a class="reference internal" href="#codecs.CodecInfo" title="codecs.CodecInfo"><code class="xref py py-class docutils literal notranslate"><span class="pre">CodecInfo</span></code></a> object is
found, a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a> is raised. Otherwise, the <a class="reference internal" href="#codecs.CodecInfo" title="codecs.CodecInfo"><code class="xref py py-class docutils literal notranslate"><span class="pre">CodecInfo</span></code></a> object
is stored in the cache and returned to the caller.</p>
</dd></dl>

<dl class="class">
<dt id="codecs.CodecInfo">
<em class="property">class </em><code class="descclassname">codecs.</code><code class="descname">CodecInfo</code><span class="sig-paren">(</span><em>encode</em>, <em>decode</em>, <em>streamreader=None</em>, <em>streamwriter=None</em>, <em>incrementalencoder=None</em>, <em>incrementaldecoder=None</em>, <em>name=None</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.CodecInfo" title="永久链接至目标">¶</a></dt>
<dd><p>Codec details when looking up the codec registry. The constructor
arguments are stored in attributes of the same name:</p>
<dl class="attribute">
<dt id="codecs.CodecInfo.name">
<code class="descname">name</code><a class="headerlink" href="#codecs.CodecInfo.name" title="永久链接至目标">¶</a></dt>
<dd><p>The name of the encoding.</p>
</dd></dl>

<dl class="attribute">
<dt id="codecs.CodecInfo.encode">
<code class="descname">encode</code><a class="headerlink" href="#codecs.CodecInfo.encode" title="永久链接至目标">¶</a></dt>
<dt id="codecs.CodecInfo.decode">
<code class="descname">decode</code><a class="headerlink" href="#codecs.CodecInfo.decode" title="永久链接至目标">¶</a></dt>
<dd><p>The stateless encoding and decoding functions. These must be
functions or methods which have the same interface as
the <a class="reference internal" href="#codecs.Codec.encode" title="codecs.Codec.encode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">encode()</span></code></a> and <a class="reference internal" href="#codecs.Codec.decode" title="codecs.Codec.decode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">decode()</span></code></a> methods of Codec
instances (see <a class="reference internal" href="#codec-objects"><span class="std std-ref">Codec Interface</span></a>).
The functions or methods are expected to work in a stateless mode.</p>
</dd></dl>

<dl class="attribute">
<dt id="codecs.CodecInfo.incrementalencoder">
<code class="descname">incrementalencoder</code><a class="headerlink" href="#codecs.CodecInfo.incrementalencoder" title="永久链接至目标">¶</a></dt>
<dt id="codecs.CodecInfo.incrementaldecoder">
<code class="descname">incrementaldecoder</code><a class="headerlink" href="#codecs.CodecInfo.incrementaldecoder" title="永久链接至目标">¶</a></dt>
<dd><p>Incremental encoder and decoder classes or factory functions.
These have to provide the interface defined by the base classes
<a class="reference internal" href="#codecs.IncrementalEncoder" title="codecs.IncrementalEncoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalEncoder</span></code></a> and <a class="reference internal" href="#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalDecoder</span></code></a>,
respectively. Incremental codecs can maintain state.</p>
</dd></dl>

<dl class="attribute">
<dt id="codecs.CodecInfo.streamwriter">
<code class="descname">streamwriter</code><a class="headerlink" href="#codecs.CodecInfo.streamwriter" title="永久链接至目标">¶</a></dt>
<dt id="codecs.CodecInfo.streamreader">
<code class="descname">streamreader</code><a class="headerlink" href="#codecs.CodecInfo.streamreader" title="永久链接至目标">¶</a></dt>
<dd><p>Stream writer and reader classes or factory functions. These have to
provide the interface defined by the base classes
<a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> and <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a>, respectively.
Stream codecs can maintain state.</p>
</dd></dl>

</dd></dl>

<p>To simplify access to the various codec components, the module provides
these additional functions which use <a class="reference internal" href="#codecs.lookup" title="codecs.lookup"><code class="xref py py-func docutils literal notranslate"><span class="pre">lookup()</span></code></a> for the codec lookup:</p>
<dl class="function">
<dt id="codecs.getencoder">
<code class="descclassname">codecs.</code><code class="descname">getencoder</code><span class="sig-paren">(</span><em>encoding</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.getencoder" title="永久链接至目标">¶</a></dt>
<dd><p>Look up the codec for the given encoding and return its encoder function.</p>
<p>Raises a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a> in case the encoding cannot be found.</p>
</dd></dl>

<dl class="function">
<dt id="codecs.getdecoder">
<code class="descclassname">codecs.</code><code class="descname">getdecoder</code><span class="sig-paren">(</span><em>encoding</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.getdecoder" title="永久链接至目标">¶</a></dt>
<dd><p>Look up the codec for the given encoding and return its decoder function.</p>
<p>Raises a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a> in case the encoding cannot be found.</p>
</dd></dl>

<dl class="function">
<dt id="codecs.getincrementalencoder">
<code class="descclassname">codecs.</code><code class="descname">getincrementalencoder</code><span class="sig-paren">(</span><em>encoding</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.getincrementalencoder" title="永久链接至目标">¶</a></dt>
<dd><p>Look up the codec for the given encoding and return its incremental encoder
class or factory function.</p>
<p>Raises a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a> in case the encoding cannot be found or the codec
doesn't support an incremental encoder.</p>
</dd></dl>

<dl class="function">
<dt id="codecs.getincrementaldecoder">
<code class="descclassname">codecs.</code><code class="descname">getincrementaldecoder</code><span class="sig-paren">(</span><em>encoding</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.getincrementaldecoder" title="永久链接至目标">¶</a></dt>
<dd><p>Look up the codec for the given encoding and return its incremental decoder
class or factory function.</p>
<p>Raises a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a> in case the encoding cannot be found or the codec
doesn't support an incremental decoder.</p>
</dd></dl>

<dl class="function">
<dt id="codecs.getreader">
<code class="descclassname">codecs.</code><code class="descname">getreader</code><span class="sig-paren">(</span><em>encoding</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.getreader" title="永久链接至目标">¶</a></dt>
<dd><p>Look up the codec for the given encoding and return its <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a>
class or factory function.</p>
<p>Raises a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a> in case the encoding cannot be found.</p>
</dd></dl>

<dl class="function">
<dt id="codecs.getwriter">
<code class="descclassname">codecs.</code><code class="descname">getwriter</code><span class="sig-paren">(</span><em>encoding</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.getwriter" title="永久链接至目标">¶</a></dt>
<dd><p>Look up the codec for the given encoding and return its <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a>
class or factory function.</p>
<p>Raises a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a> in case the encoding cannot be found.</p>
</dd></dl>

<p>Custom codecs are made available by registering a suitable codec search
function:</p>
<dl class="function">
<dt id="codecs.register">
<code class="descclassname">codecs.</code><code class="descname">register</code><span class="sig-paren">(</span><em>search_function</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.register" title="永久链接至目标">¶</a></dt>
<dd><p>Register a codec search function. Search functions are expected to take one
argument, being the encoding name in all lower case letters, and return a
<a class="reference internal" href="#codecs.CodecInfo" title="codecs.CodecInfo"><code class="xref py py-class docutils literal notranslate"><span class="pre">CodecInfo</span></code></a> object. In case a search function cannot find
a given encoding, it should return <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
<div class="admonition note">
<p class="first admonition-title">注解</p>
<p class="last">Search function registration is not currently reversible,
which may cause problems in some cases, such as unit testing or
module reloading.</p>
</div>
</dd></dl>

<p>While the builtin <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> and the associated <a class="reference internal" href="io.html#module-io" title="io: Core tools for working with streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">io</span></code></a> module are the
recommended approach for working with encoded text files, this module
provides additional utility functions and classes that allow the use of a
wider range of codecs when working with binary files:</p>
<dl class="function">
<dt id="codecs.open">
<code class="descclassname">codecs.</code><code class="descname">open</code><span class="sig-paren">(</span><em>filename</em>, <em>mode='r'</em>, <em>encoding=None</em>, <em>errors='strict'</em>, <em>buffering=1</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.open" title="永久链接至目标">¶</a></dt>
<dd><p>Open an encoded file using the given <em>mode</em> and return an instance of
<a class="reference internal" href="#codecs.StreamReaderWriter" title="codecs.StreamReaderWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReaderWriter</span></code></a>, providing transparent encoding/decoding.
The default file mode is <code class="docutils literal notranslate"><span class="pre">'r'</span></code>, meaning to open the file in read mode.</p>
<div class="admonition note">
<p class="first admonition-title">注解</p>
<p class="last">Underlying encoded files are always opened in binary mode.
No automatic conversion of <code class="docutils literal notranslate"><span class="pre">'\n'</span></code> is done on reading and writing.
The <em>mode</em> argument may be any binary mode acceptable to the built-in
<a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> function; the <code class="docutils literal notranslate"><span class="pre">'b'</span></code> is automatically added.</p>
</div>
<p><em>encoding</em> specifies the encoding which is to be used for the file.
Any encoding that encodes to and decodes from bytes is allowed, and
the data types supported by the file methods depend on the codec used.</p>
<p><em>errors</em> may be given to define the error handling. It defaults to <code class="docutils literal notranslate"><span class="pre">'strict'</span></code>
which causes a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> to be raised in case an encoding error occurs.</p>
<p><em>buffering</em> has the same meaning as for the built-in <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> function.  It
defaults to line buffered.</p>
</dd></dl>

<dl class="function">
<dt id="codecs.EncodedFile">
<code class="descclassname">codecs.</code><code class="descname">EncodedFile</code><span class="sig-paren">(</span><em>file</em>, <em>data_encoding</em>, <em>file_encoding=None</em>, <em>errors='strict'</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.EncodedFile" title="永久链接至目标">¶</a></dt>
<dd><p>Return a <a class="reference internal" href="#codecs.StreamRecoder" title="codecs.StreamRecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamRecoder</span></code></a> instance, a wrapped version of <em>file</em>
which provides transparent transcoding. The original file is closed
when the wrapped version is closed.</p>
<p>Data written to the wrapped file is decoded according to the given
<em>data_encoding</em> and then written to the original file as bytes using
<em>file_encoding</em>. Bytes read from the original file are decoded
according to <em>file_encoding</em>, and the result is encoded
using <em>data_encoding</em>.</p>
<p>If <em>file_encoding</em> is not given, it defaults to <em>data_encoding</em>.</p>
<p><em>errors</em> may be given to define the error handling. It defaults to
<code class="docutils literal notranslate"><span class="pre">'strict'</span></code>, which causes <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> to be raised in case an encoding
error occurs.</p>
</dd></dl>

<dl class="function">
<dt id="codecs.iterencode">
<code class="descclassname">codecs.</code><code class="descname">iterencode</code><span class="sig-paren">(</span><em>iterator</em>, <em>encoding</em>, <em>errors='strict'</em>, <em>**kwargs</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.iterencode" title="永久链接至目标">¶</a></dt>
<dd><p>Uses an incremental encoder to iteratively encode the input provided by
<em>iterator</em>. This function is a <a class="reference internal" href="../glossary.html#term-generator"><span class="xref std std-term">generator</span></a>.
The <em>errors</em> argument (as well as any
other keyword argument) is passed through to the incremental encoder.</p>
<p>This function requires that the codec accept text <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> objects
to encode. Therefore it does not support bytes-to-bytes encoders such as
<code class="docutils literal notranslate"><span class="pre">base64_codec</span></code>.</p>
</dd></dl>

<dl class="function">
<dt id="codecs.iterdecode">
<code class="descclassname">codecs.</code><code class="descname">iterdecode</code><span class="sig-paren">(</span><em>iterator</em>, <em>encoding</em>, <em>errors='strict'</em>, <em>**kwargs</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.iterdecode" title="永久链接至目标">¶</a></dt>
<dd><p>Uses an incremental decoder to iteratively decode the input provided by
<em>iterator</em>. This function is a <a class="reference internal" href="../glossary.html#term-generator"><span class="xref std std-term">generator</span></a>.
The <em>errors</em> argument (as well as any
other keyword argument) is passed through to the incremental decoder.</p>
<p>This function requires that the codec accept <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> objects
to decode. Therefore it does not support text-to-text encoders such as
<code class="docutils literal notranslate"><span class="pre">rot_13</span></code>, although <code class="docutils literal notranslate"><span class="pre">rot_13</span></code> may be used equivalently with
<a class="reference internal" href="#codecs.iterencode" title="codecs.iterencode"><code class="xref py py-func docutils literal notranslate"><span class="pre">iterencode()</span></code></a>.</p>
</dd></dl>

<p>The module also provides the following constants which are useful for reading
and writing to platform dependent files:</p>
<dl class="data">
<dt id="codecs.BOM">
<code class="descclassname">codecs.</code><code class="descname">BOM</code><a class="headerlink" href="#codecs.BOM" title="永久链接至目标">¶</a></dt>
<dt id="codecs.BOM_BE">
<code class="descclassname">codecs.</code><code class="descname">BOM_BE</code><a class="headerlink" href="#codecs.BOM_BE" title="永久链接至目标">¶</a></dt>
<dt id="codecs.BOM_LE">
<code class="descclassname">codecs.</code><code class="descname">BOM_LE</code><a class="headerlink" href="#codecs.BOM_LE" title="永久链接至目标">¶</a></dt>
<dt id="codecs.BOM_UTF8">
<code class="descclassname">codecs.</code><code class="descname">BOM_UTF8</code><a class="headerlink" href="#codecs.BOM_UTF8" title="永久链接至目标">¶</a></dt>
<dt id="codecs.BOM_UTF16">
<code class="descclassname">codecs.</code><code class="descname">BOM_UTF16</code><a class="headerlink" href="#codecs.BOM_UTF16" title="永久链接至目标">¶</a></dt>
<dt id="codecs.BOM_UTF16_BE">
<code class="descclassname">codecs.</code><code class="descname">BOM_UTF16_BE</code><a class="headerlink" href="#codecs.BOM_UTF16_BE" title="永久链接至目标">¶</a></dt>
<dt id="codecs.BOM_UTF16_LE">
<code class="descclassname">codecs.</code><code class="descname">BOM_UTF16_LE</code><a class="headerlink" href="#codecs.BOM_UTF16_LE" title="永久链接至目标">¶</a></dt>
<dt id="codecs.BOM_UTF32">
<code class="descclassname">codecs.</code><code class="descname">BOM_UTF32</code><a class="headerlink" href="#codecs.BOM_UTF32" title="永久链接至目标">¶</a></dt>
<dt id="codecs.BOM_UTF32_BE">
<code class="descclassname">codecs.</code><code class="descname">BOM_UTF32_BE</code><a class="headerlink" href="#codecs.BOM_UTF32_BE" title="永久链接至目标">¶</a></dt>
<dt id="codecs.BOM_UTF32_LE">
<code class="descclassname">codecs.</code><code class="descname">BOM_UTF32_LE</code><a class="headerlink" href="#codecs.BOM_UTF32_LE" title="永久链接至目标">¶</a></dt>
<dd><p>These constants define various byte sequences,
being Unicode byte order marks (BOMs) for several encodings. They are
used in UTF-16 and UTF-32 data streams to indicate the byte order used,
and in UTF-8 as a Unicode signature. <a class="reference internal" href="#codecs.BOM_UTF16" title="codecs.BOM_UTF16"><code class="xref py py-const docutils literal notranslate"><span class="pre">BOM_UTF16</span></code></a> is either
<a class="reference internal" href="#codecs.BOM_UTF16_BE" title="codecs.BOM_UTF16_BE"><code class="xref py py-const docutils literal notranslate"><span class="pre">BOM_UTF16_BE</span></code></a> or <a class="reference internal" href="#codecs.BOM_UTF16_LE" title="codecs.BOM_UTF16_LE"><code class="xref py py-const docutils literal notranslate"><span class="pre">BOM_UTF16_LE</span></code></a> depending on the platform's
native byte order, <a class="reference internal" href="#codecs.BOM" title="codecs.BOM"><code class="xref py py-const docutils literal notranslate"><span class="pre">BOM</span></code></a> is an alias for <a class="reference internal" href="#codecs.BOM_UTF16" title="codecs.BOM_UTF16"><code class="xref py py-const docutils literal notranslate"><span class="pre">BOM_UTF16</span></code></a>,
<a class="reference internal" href="#codecs.BOM_LE" title="codecs.BOM_LE"><code class="xref py py-const docutils literal notranslate"><span class="pre">BOM_LE</span></code></a> for <a class="reference internal" href="#codecs.BOM_UTF16_LE" title="codecs.BOM_UTF16_LE"><code class="xref py py-const docutils literal notranslate"><span class="pre">BOM_UTF16_LE</span></code></a> and <a class="reference internal" href="#codecs.BOM_BE" title="codecs.BOM_BE"><code class="xref py py-const docutils literal notranslate"><span class="pre">BOM_BE</span></code></a> for
<a class="reference internal" href="#codecs.BOM_UTF16_BE" title="codecs.BOM_UTF16_BE"><code class="xref py py-const docutils literal notranslate"><span class="pre">BOM_UTF16_BE</span></code></a>. The others represent the BOM in UTF-8 and UTF-32
encodings.</p>
</dd></dl>

<div class="section" id="codec-base-classes">
<span id="id1"></span><h2>Codec Base Classes<a class="headerlink" href="#codec-base-classes" title="永久链接至标题">¶</a></h2>
<p>The <a class="reference internal" href="#module-codecs" title="codecs: Encode and decode data and streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">codecs</span></code></a> module defines a set of base classes which define the
interfaces for working with codec objects, and can also be used as the basis
for custom codec implementations.</p>
<p>Each codec has to define four interfaces to make it usable as codec in Python:
stateless encoder, stateless decoder, stream reader and stream writer. The
stream reader and writers typically reuse the stateless encoder/decoder to
implement the file protocols. Codec authors also need to define how the
codec will handle encoding and decoding errors.</p>
<div class="section" id="error-handlers">
<span id="surrogateescape"></span><span id="id2"></span><h3>Error Handlers<a class="headerlink" href="#error-handlers" title="永久链接至标题">¶</a></h3>
<p>To simplify and standardize error handling,
codecs may implement different error handling schemes by
accepting the <em>errors</em> string argument.  The following string values are
defined and implemented by all standard Python codecs:</p>
<table border="1" class="docutils">
<colgroup>
<col width="35%" />
<col width="65%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">值</th>
<th class="head">意义</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">'strict'</span></code></td>
<td>Raise <a class="reference internal" href="exceptions.html#UnicodeError" title="UnicodeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnicodeError</span></code></a> (or a subclass);
this is the default.  Implemented in
<a class="reference internal" href="#codecs.strict_errors" title="codecs.strict_errors"><code class="xref py py-func docutils literal notranslate"><span class="pre">strict_errors()</span></code></a>.</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">'ignore'</span></code></td>
<td>Ignore the malformed data and continue
without further notice.  Implemented in
<a class="reference internal" href="#codecs.ignore_errors" title="codecs.ignore_errors"><code class="xref py py-func docutils literal notranslate"><span class="pre">ignore_errors()</span></code></a>.</td>
</tr>
</tbody>
</table>
<p>The following error handlers are only applicable to
<a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encodings</span></a>:</p>
<table border="1" class="docutils" id="index-1">
<colgroup>
<col width="35%" />
<col width="65%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">值</th>
<th class="head">意义</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">'replace'</span></code></td>
<td>Replace with a suitable replacement
marker; Python will use the official
<code class="docutils literal notranslate"><span class="pre">U+FFFD</span></code> REPLACEMENT CHARACTER for the
built-in codecs on decoding, and '?' on
encoding.  Implemented in
<a class="reference internal" href="#codecs.replace_errors" title="codecs.replace_errors"><code class="xref py py-func docutils literal notranslate"><span class="pre">replace_errors()</span></code></a>.</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">'xmlcharrefreplace'</span></code></td>
<td>Replace with the appropriate XML character
reference (only for encoding).  Implemented
in <a class="reference internal" href="#codecs.xmlcharrefreplace_errors" title="codecs.xmlcharrefreplace_errors"><code class="xref py py-func docutils literal notranslate"><span class="pre">xmlcharrefreplace_errors()</span></code></a>.</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">'backslashreplace'</span></code></td>
<td>Replace with backslashed escape sequences.
Implemented in
<a class="reference internal" href="#codecs.backslashreplace_errors" title="codecs.backslashreplace_errors"><code class="xref py py-func docutils literal notranslate"><span class="pre">backslashreplace_errors()</span></code></a>.</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">'namereplace'</span></code></td>
<td>Replace with <code class="docutils literal notranslate"><span class="pre">\N{...}</span></code> escape sequences
(only for encoding).  Implemented in
<a class="reference internal" href="#codecs.namereplace_errors" title="codecs.namereplace_errors"><code class="xref py py-func docutils literal notranslate"><span class="pre">namereplace_errors()</span></code></a>.</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">'surrogateescape'</span></code></td>
<td>On decoding, replace byte with individual
surrogate code ranging from <code class="docutils literal notranslate"><span class="pre">U+DC80</span></code> to
<code class="docutils literal notranslate"><span class="pre">U+DCFF</span></code>.  This code will then be turned
back into the same byte when the
<code class="docutils literal notranslate"><span class="pre">'surrogateescape'</span></code> error handler is used
when encoding the data.  (See <span class="target" id="index-2"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0383"><strong>PEP 383</strong></a> for
more.)</td>
</tr>
</tbody>
</table>
<p>In addition, the following error handler is specific to the given codecs:</p>
<table border="1" class="docutils">
<colgroup>
<col width="22%" />
<col width="28%" />
<col width="50%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">值</th>
<th class="head">Codecs</th>
<th class="head">意义</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">'surrogatepass'</span></code></td>
<td>utf-8, utf-16, utf-32,
utf-16-be, utf-16-le,
utf-32-be, utf-32-le</td>
<td>Allow encoding and decoding of surrogate
codes.  These codecs normally treat the
presence of surrogates as an error.</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">3.1 新版功能: </span>The <code class="docutils literal notranslate"><span class="pre">'surrogateescape'</span></code> and <code class="docutils literal notranslate"><span class="pre">'surrogatepass'</span></code> error handlers.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">在 3.4 版更改: </span>The <code class="docutils literal notranslate"><span class="pre">'surrogatepass'</span></code> error handlers now works with utf-16* and utf-32* codecs.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified">3.5 新版功能: </span>The <code class="docutils literal notranslate"><span class="pre">'namereplace'</span></code> error handler.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">在 3.5 版更改: </span>The <code class="docutils literal notranslate"><span class="pre">'backslashreplace'</span></code> error handlers now works with decoding and
translating.</p>
</div>
<p>The set of allowed values can be extended by registering a new named error
handler:</p>
<dl class="function">
<dt id="codecs.register_error">
<code class="descclassname">codecs.</code><code class="descname">register_error</code><span class="sig-paren">(</span><em>name</em>, <em>error_handler</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.register_error" title="永久链接至目标">¶</a></dt>
<dd><p>Register the error handling function <em>error_handler</em> under the name <em>name</em>.
The <em>error_handler</em> argument will be called during encoding and decoding
in case of an error, when <em>name</em> is specified as the errors parameter.</p>
<p>For encoding, <em>error_handler</em> will be called with a <a class="reference internal" href="exceptions.html#UnicodeEncodeError" title="UnicodeEncodeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnicodeEncodeError</span></code></a>
instance, which contains information about the location of the error. The
error handler must either raise this or a different exception, or return a
tuple with a replacement for the unencodable part of the input and a position
where encoding should continue. The replacement may be either <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> or
<a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a>.  If the replacement is bytes, the encoder will simply copy
them into the output buffer. If the replacement is a string, the encoder will
encode the replacement.  Encoding continues on original input at the
specified position. Negative position values will be treated as being
relative to the end of the input string. If the resulting position is out of
bound an <a class="reference internal" href="exceptions.html#IndexError" title="IndexError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IndexError</span></code></a> will be raised.</p>
<p>Decoding and translating works similarly, except <a class="reference internal" href="exceptions.html#UnicodeDecodeError" title="UnicodeDecodeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnicodeDecodeError</span></code></a> or
<a class="reference internal" href="exceptions.html#UnicodeTranslateError" title="UnicodeTranslateError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnicodeTranslateError</span></code></a> will be passed to the handler and that the
replacement from the error handler will be put into the output directly.</p>
</dd></dl>

<p>Previously registered error handlers (including the standard error handlers)
can be looked up by name:</p>
<dl class="function">
<dt id="codecs.lookup_error">
<code class="descclassname">codecs.</code><code class="descname">lookup_error</code><span class="sig-paren">(</span><em>name</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.lookup_error" title="永久链接至目标">¶</a></dt>
<dd><p>Return the error handler previously registered under the name <em>name</em>.</p>
<p>Raises a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a> in case the handler cannot be found.</p>
</dd></dl>

<p>The following standard error handlers are also made available as module level
functions:</p>
<dl class="function">
<dt id="codecs.strict_errors">
<code class="descclassname">codecs.</code><code class="descname">strict_errors</code><span class="sig-paren">(</span><em>exception</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.strict_errors" title="永久链接至目标">¶</a></dt>
<dd><p>Implements the <code class="docutils literal notranslate"><span class="pre">'strict'</span></code> error handling: each encoding or
decoding error raises a <a class="reference internal" href="exceptions.html#UnicodeError" title="UnicodeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnicodeError</span></code></a>.</p>
</dd></dl>

<dl class="function">
<dt id="codecs.replace_errors">
<code class="descclassname">codecs.</code><code class="descname">replace_errors</code><span class="sig-paren">(</span><em>exception</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.replace_errors" title="永久链接至目标">¶</a></dt>
<dd><p>Implements the <code class="docutils literal notranslate"><span class="pre">'replace'</span></code> error handling (for <a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encodings</span></a> only): substitutes <code class="docutils literal notranslate"><span class="pre">'?'</span></code> for encoding errors
(to be encoded by the codec), and <code class="docutils literal notranslate"><span class="pre">'\ufffd'</span></code> (the Unicode replacement
character) for decoding errors.</p>
</dd></dl>

<dl class="function">
<dt id="codecs.ignore_errors">
<code class="descclassname">codecs.</code><code class="descname">ignore_errors</code><span class="sig-paren">(</span><em>exception</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.ignore_errors" title="永久链接至目标">¶</a></dt>
<dd><p>Implements the <code class="docutils literal notranslate"><span class="pre">'ignore'</span></code> error handling: malformed data is ignored and
encoding or decoding is continued without further notice.</p>
</dd></dl>

<dl class="function">
<dt id="codecs.xmlcharrefreplace_errors">
<code class="descclassname">codecs.</code><code class="descname">xmlcharrefreplace_errors</code><span class="sig-paren">(</span><em>exception</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.xmlcharrefreplace_errors" title="永久链接至目标">¶</a></dt>
<dd><p>Implements the <code class="docutils literal notranslate"><span class="pre">'xmlcharrefreplace'</span></code> error handling (for encoding with
<a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encodings</span></a> only): the
unencodable character is replaced by an appropriate XML character reference.</p>
</dd></dl>

<dl class="function">
<dt id="codecs.backslashreplace_errors">
<code class="descclassname">codecs.</code><code class="descname">backslashreplace_errors</code><span class="sig-paren">(</span><em>exception</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.backslashreplace_errors" title="永久链接至目标">¶</a></dt>
<dd><p>Implements the <code class="docutils literal notranslate"><span class="pre">'backslashreplace'</span></code> error handling (for
<a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encodings</span></a> only): malformed data is
replaced by a backslashed escape sequence.</p>
</dd></dl>

<dl class="function">
<dt id="codecs.namereplace_errors">
<code class="descclassname">codecs.</code><code class="descname">namereplace_errors</code><span class="sig-paren">(</span><em>exception</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.namereplace_errors" title="永久链接至目标">¶</a></dt>
<dd><p>Implements the <code class="docutils literal notranslate"><span class="pre">'namereplace'</span></code> error handling (for encoding with
<a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encodings</span></a> only): the
unencodable character is replaced by a <code class="docutils literal notranslate"><span class="pre">\N{...}</span></code> escape sequence.</p>
<div class="versionadded">
<p><span class="versionmodified">3.5 新版功能.</span></p>
</div>
</dd></dl>

</div>
<div class="section" id="stateless-encoding-and-decoding">
<span id="codec-objects"></span><h3>Stateless Encoding and Decoding<a class="headerlink" href="#stateless-encoding-and-decoding" title="永久链接至标题">¶</a></h3>
<p>The base <code class="xref py py-class docutils literal notranslate"><span class="pre">Codec</span></code> class defines these methods which also define the
function interfaces of the stateless encoder and decoder:</p>
<dl class="method">
<dt id="codecs.Codec.encode">
<code class="descclassname">Codec.</code><code class="descname">encode</code><span class="sig-paren">(</span><em>input</em><span class="optional">[</span>, <em>errors</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.Codec.encode" title="永久链接至目标">¶</a></dt>
<dd><p>Encodes the object <em>input</em> and returns a tuple (output object, length consumed).
For instance, <a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encoding</span></a> converts
a string object to a bytes object using a particular
character set encoding (e.g., <code class="docutils literal notranslate"><span class="pre">cp1252</span></code> or <code class="docutils literal notranslate"><span class="pre">iso-8859-1</span></code>).</p>
<p>The <em>errors</em> argument defines the error handling to apply.
It defaults to <code class="docutils literal notranslate"><span class="pre">'strict'</span></code> handling.</p>
<p>The method may not store state in the <code class="xref py py-class docutils literal notranslate"><span class="pre">Codec</span></code> instance. Use
<a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> for codecs which have to keep state in order to make
encoding efficient.</p>
<p>The encoder must be able to handle zero length input and return an empty object
of the output object type in this situation.</p>
</dd></dl>

<dl class="method">
<dt id="codecs.Codec.decode">
<code class="descclassname">Codec.</code><code class="descname">decode</code><span class="sig-paren">(</span><em>input</em><span class="optional">[</span>, <em>errors</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.Codec.decode" title="永久链接至目标">¶</a></dt>
<dd><p>Decodes the object <em>input</em> and returns a tuple (output object, length
consumed).  For instance, for a <a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encoding</span></a>, decoding converts
a bytes object encoded using a particular
character set encoding to a string object.</p>
<p>For text encodings and bytes-to-bytes codecs,
<em>input</em> must be a bytes object or one which provides the read-only
buffer interface -- for example, buffer objects and memory mapped files.</p>
<p>The <em>errors</em> argument defines the error handling to apply.
It defaults to <code class="docutils literal notranslate"><span class="pre">'strict'</span></code> handling.</p>
<p>The method may not store state in the <code class="xref py py-class docutils literal notranslate"><span class="pre">Codec</span></code> instance. Use
<a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> for codecs which have to keep state in order to make
decoding efficient.</p>
<p>The decoder must be able to handle zero length input and return an empty object
of the output object type in this situation.</p>
</dd></dl>

</div>
<div class="section" id="incremental-encoding-and-decoding">
<h3>Incremental Encoding and Decoding<a class="headerlink" href="#incremental-encoding-and-decoding" title="永久链接至标题">¶</a></h3>
<p>The <a class="reference internal" href="#codecs.IncrementalEncoder" title="codecs.IncrementalEncoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalEncoder</span></code></a> and <a class="reference internal" href="#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalDecoder</span></code></a> classes provide
the basic interface for incremental encoding and decoding. Encoding/decoding the
input isn't done with one call to the stateless encoder/decoder function, but
with multiple calls to the
<a class="reference internal" href="#codecs.IncrementalEncoder.encode" title="codecs.IncrementalEncoder.encode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">encode()</span></code></a>/<a class="reference internal" href="#codecs.IncrementalDecoder.decode" title="codecs.IncrementalDecoder.decode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">decode()</span></code></a> method of
the incremental encoder/decoder. The incremental encoder/decoder keeps track of
the encoding/decoding process during method calls.</p>
<p>The joined output of calls to the
<a class="reference internal" href="#codecs.IncrementalEncoder.encode" title="codecs.IncrementalEncoder.encode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">encode()</span></code></a>/<a class="reference internal" href="#codecs.IncrementalDecoder.decode" title="codecs.IncrementalDecoder.decode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">decode()</span></code></a> method is
the same as if all the single inputs were joined into one, and this input was
encoded/decoded with the stateless encoder/decoder.</p>
<div class="section" id="incrementalencoder-objects">
<span id="incremental-encoder-objects"></span><h4>IncrementalEncoder Objects<a class="headerlink" href="#incrementalencoder-objects" title="永久链接至标题">¶</a></h4>
<p>The <a class="reference internal" href="#codecs.IncrementalEncoder" title="codecs.IncrementalEncoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalEncoder</span></code></a> class is used for encoding an input in multiple
steps. It defines the following methods which every incremental encoder must
define in order to be compatible with the Python codec registry.</p>
<dl class="class">
<dt id="codecs.IncrementalEncoder">
<em class="property">class </em><code class="descclassname">codecs.</code><code class="descname">IncrementalEncoder</code><span class="sig-paren">(</span><em>errors='strict'</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalEncoder" title="永久链接至目标">¶</a></dt>
<dd><p>Constructor for an <a class="reference internal" href="#codecs.IncrementalEncoder" title="codecs.IncrementalEncoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalEncoder</span></code></a> instance.</p>
<p>All incremental encoders must provide this constructor interface. They are free
to add additional keyword arguments, but only the ones defined here are used by
the Python codec registry.</p>
<p>The <a class="reference internal" href="#codecs.IncrementalEncoder" title="codecs.IncrementalEncoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalEncoder</span></code></a> may implement different error handling schemes
by providing the <em>errors</em> keyword argument. See <a class="reference internal" href="#error-handlers"><span class="std std-ref">Error Handlers</span></a> for
possible values.</p>
<p>The <em>errors</em> argument will be assigned to an attribute of the same name.
Assigning to this attribute makes it possible to switch between different error
handling strategies during the lifetime of the <a class="reference internal" href="#codecs.IncrementalEncoder" title="codecs.IncrementalEncoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalEncoder</span></code></a>
object.</p>
<dl class="method">
<dt id="codecs.IncrementalEncoder.encode">
<code class="descname">encode</code><span class="sig-paren">(</span><em>object</em><span class="optional">[</span>, <em>final</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalEncoder.encode" title="永久链接至目标">¶</a></dt>
<dd><p>Encodes <em>object</em> (taking the current state of the encoder into account)
and returns the resulting encoded object. If this is the last call to
<a class="reference internal" href="#codecs.encode" title="codecs.encode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">encode()</span></code></a> <em>final</em> must be true (the default is false).</p>
</dd></dl>

<dl class="method">
<dt id="codecs.IncrementalEncoder.reset">
<code class="descname">reset</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalEncoder.reset" title="永久链接至目标">¶</a></dt>
<dd><p>Reset the encoder to the initial state. The output is discarded: call
<code class="docutils literal notranslate"><span class="pre">.encode(object,</span> <span class="pre">final=True)</span></code>, passing an empty byte or text string
if necessary, to reset the encoder and to get the output.</p>
</dd></dl>

<dl class="method">
<dt id="codecs.IncrementalEncoder.getstate">
<code class="descname">getstate</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalEncoder.getstate" title="永久链接至目标">¶</a></dt>
<dd><p>Return the current state of the encoder which must be an integer. The
implementation should make sure that <code class="docutils literal notranslate"><span class="pre">0</span></code> is the most common
state. (States that are more complicated than integers can be converted
into an integer by marshaling/pickling the state and encoding the bytes
of the resulting string into an integer).</p>
</dd></dl>

<dl class="method">
<dt id="codecs.IncrementalEncoder.setstate">
<code class="descname">setstate</code><span class="sig-paren">(</span><em>state</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalEncoder.setstate" title="永久链接至目标">¶</a></dt>
<dd><p>Set the state of the encoder to <em>state</em>. <em>state</em> must be an encoder state
returned by <a class="reference internal" href="#codecs.IncrementalEncoder.getstate" title="codecs.IncrementalEncoder.getstate"><code class="xref py py-meth docutils literal notranslate"><span class="pre">getstate()</span></code></a>.</p>
</dd></dl>

</dd></dl>

</div>
<div class="section" id="incrementaldecoder-objects">
<span id="incremental-decoder-objects"></span><h4>IncrementalDecoder Objects<a class="headerlink" href="#incrementaldecoder-objects" title="永久链接至标题">¶</a></h4>
<p>The <a class="reference internal" href="#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalDecoder</span></code></a> class is used for decoding an input in multiple
steps. It defines the following methods which every incremental decoder must
define in order to be compatible with the Python codec registry.</p>
<dl class="class">
<dt id="codecs.IncrementalDecoder">
<em class="property">class </em><code class="descclassname">codecs.</code><code class="descname">IncrementalDecoder</code><span class="sig-paren">(</span><em>errors='strict'</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalDecoder" title="永久链接至目标">¶</a></dt>
<dd><p>Constructor for an <a class="reference internal" href="#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalDecoder</span></code></a> instance.</p>
<p>All incremental decoders must provide this constructor interface. They are free
to add additional keyword arguments, but only the ones defined here are used by
the Python codec registry.</p>
<p>The <a class="reference internal" href="#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalDecoder</span></code></a> may implement different error handling schemes
by providing the <em>errors</em> keyword argument. See <a class="reference internal" href="#error-handlers"><span class="std std-ref">Error Handlers</span></a> for
possible values.</p>
<p>The <em>errors</em> argument will be assigned to an attribute of the same name.
Assigning to this attribute makes it possible to switch between different error
handling strategies during the lifetime of the <a class="reference internal" href="#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">IncrementalDecoder</span></code></a>
object.</p>
<dl class="method">
<dt id="codecs.IncrementalDecoder.decode">
<code class="descname">decode</code><span class="sig-paren">(</span><em>object</em><span class="optional">[</span>, <em>final</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalDecoder.decode" title="永久链接至目标">¶</a></dt>
<dd><p>Decodes <em>object</em> (taking the current state of the decoder into account)
and returns the resulting decoded object. If this is the last call to
<a class="reference internal" href="#codecs.decode" title="codecs.decode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">decode()</span></code></a> <em>final</em> must be true (the default is false). If <em>final</em> is
true the decoder must decode the input completely and must flush all
buffers. If this isn't possible (e.g. because of incomplete byte sequences
at the end of the input) it must initiate error handling just like in the
stateless case (which might raise an exception).</p>
</dd></dl>

<dl class="method">
<dt id="codecs.IncrementalDecoder.reset">
<code class="descname">reset</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalDecoder.reset" title="永久链接至目标">¶</a></dt>
<dd><p>Reset the decoder to the initial state.</p>
</dd></dl>

<dl class="method">
<dt id="codecs.IncrementalDecoder.getstate">
<code class="descname">getstate</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalDecoder.getstate" title="永久链接至目标">¶</a></dt>
<dd><p>Return the current state of the decoder. This must be a tuple with two
items, the first must be the buffer containing the still undecoded
input. The second must be an integer and can be additional state
info. (The implementation should make sure that <code class="docutils literal notranslate"><span class="pre">0</span></code> is the most common
additional state info.) If this additional state info is <code class="docutils literal notranslate"><span class="pre">0</span></code> it must be
possible to set the decoder to the state which has no input buffered and
<code class="docutils literal notranslate"><span class="pre">0</span></code> as the additional state info, so that feeding the previously
buffered input to the decoder returns it to the previous state without
producing any output. (Additional state info that is more complicated than
integers can be converted into an integer by marshaling/pickling the info
and encoding the bytes of the resulting string into an integer.)</p>
</dd></dl>

<dl class="method">
<dt id="codecs.IncrementalDecoder.setstate">
<code class="descname">setstate</code><span class="sig-paren">(</span><em>state</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.IncrementalDecoder.setstate" title="永久链接至目标">¶</a></dt>
<dd><p>Set the state of the encoder to <em>state</em>. <em>state</em> must be a decoder state
returned by <a class="reference internal" href="#codecs.IncrementalDecoder.getstate" title="codecs.IncrementalDecoder.getstate"><code class="xref py py-meth docutils literal notranslate"><span class="pre">getstate()</span></code></a>.</p>
</dd></dl>

</dd></dl>

</div>
</div>
<div class="section" id="stream-encoding-and-decoding">
<h3>Stream Encoding and Decoding<a class="headerlink" href="#stream-encoding-and-decoding" title="永久链接至标题">¶</a></h3>
<p>The <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> and <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> classes provide generic
working interfaces which can be used to implement new encoding submodules very
easily. See <code class="xref py py-mod docutils literal notranslate"><span class="pre">encodings.utf_8</span></code> for an example of how this is done.</p>
<div class="section" id="streamwriter-objects">
<span id="stream-writer-objects"></span><h4>StreamWriter Objects<a class="headerlink" href="#streamwriter-objects" title="永久链接至标题">¶</a></h4>
<p>The <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> class is a subclass of <code class="xref py py-class docutils literal notranslate"><span class="pre">Codec</span></code> and defines the
following methods which every stream writer must define in order to be
compatible with the Python codec registry.</p>
<dl class="class">
<dt id="codecs.StreamWriter">
<em class="property">class </em><code class="descclassname">codecs.</code><code class="descname">StreamWriter</code><span class="sig-paren">(</span><em>stream</em>, <em>errors='strict'</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamWriter" title="永久链接至目标">¶</a></dt>
<dd><p>Constructor for a <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> instance.</p>
<p>All stream writers must provide this constructor interface. They are free to add
additional keyword arguments, but only the ones defined here are used by the
Python codec registry.</p>
<p>The <em>stream</em> argument must be a file-like object open for writing
text or binary data, as appropriate for the specific codec.</p>
<p>The <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> may implement different error handling schemes by
providing the <em>errors</em> keyword argument. See <a class="reference internal" href="#error-handlers"><span class="std std-ref">Error Handlers</span></a> for
the standard error handlers the underlying stream codec may support.</p>
<p>The <em>errors</em> argument will be assigned to an attribute of the same name.
Assigning to this attribute makes it possible to switch between different error
handling strategies during the lifetime of the <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> object.</p>
<dl class="method">
<dt id="codecs.StreamWriter.write">
<code class="descname">write</code><span class="sig-paren">(</span><em>object</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamWriter.write" title="永久链接至目标">¶</a></dt>
<dd><p>Writes the object's contents encoded to the stream.</p>
</dd></dl>

<dl class="method">
<dt id="codecs.StreamWriter.writelines">
<code class="descname">writelines</code><span class="sig-paren">(</span><em>list</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamWriter.writelines" title="永久链接至目标">¶</a></dt>
<dd><p>Writes the concatenated list of strings to the stream (possibly by reusing
the <a class="reference internal" href="#codecs.StreamWriter.write" title="codecs.StreamWriter.write"><code class="xref py py-meth docutils literal notranslate"><span class="pre">write()</span></code></a> method). The standard bytes-to-bytes codecs
do not support this method.</p>
</dd></dl>

<dl class="method">
<dt id="codecs.StreamWriter.reset">
<code class="descname">reset</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamWriter.reset" title="永久链接至目标">¶</a></dt>
<dd><p>Flushes and resets the codec buffers used for keeping state.</p>
<p>Calling this method should ensure that the data on the output is put into
a clean state that allows appending of new fresh data without having to
rescan the whole stream to recover state.</p>
</dd></dl>

</dd></dl>

<p>In addition to the above methods, the <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> must also inherit
all other methods and attributes from the underlying stream.</p>
</div>
<div class="section" id="streamreader-objects">
<span id="stream-reader-objects"></span><h4>StreamReader Objects<a class="headerlink" href="#streamreader-objects" title="永久链接至标题">¶</a></h4>
<p>The <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> class is a subclass of <code class="xref py py-class docutils literal notranslate"><span class="pre">Codec</span></code> and defines the
following methods which every stream reader must define in order to be
compatible with the Python codec registry.</p>
<dl class="class">
<dt id="codecs.StreamReader">
<em class="property">class </em><code class="descclassname">codecs.</code><code class="descname">StreamReader</code><span class="sig-paren">(</span><em>stream</em>, <em>errors='strict'</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamReader" title="永久链接至目标">¶</a></dt>
<dd><p>Constructor for a <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> instance.</p>
<p>All stream readers must provide this constructor interface. They are free to add
additional keyword arguments, but only the ones defined here are used by the
Python codec registry.</p>
<p>The <em>stream</em> argument must be a file-like object open for reading
text or binary data, as appropriate for the specific codec.</p>
<p>The <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> may implement different error handling schemes by
providing the <em>errors</em> keyword argument. See <a class="reference internal" href="#error-handlers"><span class="std std-ref">Error Handlers</span></a> for
the standard error handlers the underlying stream codec may support.</p>
<p>The <em>errors</em> argument will be assigned to an attribute of the same name.
Assigning to this attribute makes it possible to switch between different error
handling strategies during the lifetime of the <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> object.</p>
<p>The set of allowed values for the <em>errors</em> argument can be extended with
<a class="reference internal" href="#codecs.register_error" title="codecs.register_error"><code class="xref py py-func docutils literal notranslate"><span class="pre">register_error()</span></code></a>.</p>
<dl class="method">
<dt id="codecs.StreamReader.read">
<code class="descname">read</code><span class="sig-paren">(</span><span class="optional">[</span><em>size</em><span class="optional">[</span>, <em>chars</em><span class="optional">[</span>, <em>firstline</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamReader.read" title="永久链接至目标">¶</a></dt>
<dd><p>Decodes data from the stream and returns the resulting object.</p>
<p>The <em>chars</em> argument indicates the number of decoded
code points or bytes to return. The <a class="reference internal" href="#codecs.StreamReader.read" title="codecs.StreamReader.read"><code class="xref py py-func docutils literal notranslate"><span class="pre">read()</span></code></a> method will
never return more data than requested, but it might return less,
if there is not enough available.</p>
<p>The <em>size</em> argument indicates the approximate maximum
number of encoded bytes or code points to read
for decoding. The decoder can modify this setting as
appropriate. The default value -1 indicates to read and decode as much as
possible.  This parameter is intended to
prevent having to decode huge files in one step.</p>
<p>The <em>firstline</em> flag indicates that
it would be sufficient to only return the first
line, if there are decoding errors on later lines.</p>
<p>The method should use a greedy read strategy meaning that it should read
as much data as is allowed within the definition of the encoding and the
given size, e.g.  if optional encoding endings or state markers are
available on the stream, these should be read too.</p>
</dd></dl>

<dl class="method">
<dt id="codecs.StreamReader.readline">
<code class="descname">readline</code><span class="sig-paren">(</span><span class="optional">[</span><em>size</em><span class="optional">[</span>, <em>keepends</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamReader.readline" title="永久链接至目标">¶</a></dt>
<dd><p>Read one line from the input stream and return the decoded data.</p>
<p><em>size</em>, if given, is passed as size argument to the stream's
<a class="reference internal" href="#codecs.StreamReader.read" title="codecs.StreamReader.read"><code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code></a> method.</p>
<p>If <em>keepends</em> is false line-endings will be stripped from the lines
returned.</p>
</dd></dl>

<dl class="method">
<dt id="codecs.StreamReader.readlines">
<code class="descname">readlines</code><span class="sig-paren">(</span><span class="optional">[</span><em>sizehint</em><span class="optional">[</span>, <em>keepends</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamReader.readlines" title="永久链接至目标">¶</a></dt>
<dd><p>Read all lines available on the input stream and return them as a list of
lines.</p>
<p>Line-endings are implemented using the codec's decoder method and are
included in the list entries if <em>keepends</em> is true.</p>
<p><em>sizehint</em>, if given, is passed as the <em>size</em> argument to the stream's
<a class="reference internal" href="#codecs.StreamReader.read" title="codecs.StreamReader.read"><code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code></a> method.</p>
</dd></dl>

<dl class="method">
<dt id="codecs.StreamReader.reset">
<code class="descname">reset</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamReader.reset" title="永久链接至目标">¶</a></dt>
<dd><p>Resets the codec buffers used for keeping state.</p>
<p>Note that no stream repositioning should take place.  This method is
primarily intended to be able to recover from decoding errors.</p>
</dd></dl>

</dd></dl>

<p>In addition to the above methods, the <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> must also inherit
all other methods and attributes from the underlying stream.</p>
</div>
<div class="section" id="streamreaderwriter-objects">
<span id="stream-reader-writer"></span><h4>StreamReaderWriter Objects<a class="headerlink" href="#streamreaderwriter-objects" title="永久链接至标题">¶</a></h4>
<p>The <a class="reference internal" href="#codecs.StreamReaderWriter" title="codecs.StreamReaderWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReaderWriter</span></code></a> is a convenience class that allows wrapping
streams which work in both read and write modes.</p>
<p>The design is such that one can use the factory functions returned by the
<a class="reference internal" href="#codecs.lookup" title="codecs.lookup"><code class="xref py py-func docutils literal notranslate"><span class="pre">lookup()</span></code></a> function to construct the instance.</p>
<dl class="class">
<dt id="codecs.StreamReaderWriter">
<em class="property">class </em><code class="descclassname">codecs.</code><code class="descname">StreamReaderWriter</code><span class="sig-paren">(</span><em>stream</em>, <em>Reader</em>, <em>Writer</em>, <em>errors='strict'</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamReaderWriter" title="永久链接至目标">¶</a></dt>
<dd><p>Creates a <a class="reference internal" href="#codecs.StreamReaderWriter" title="codecs.StreamReaderWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReaderWriter</span></code></a> instance. <em>stream</em> must be a file-like
object. <em>Reader</em> and <em>Writer</em> must be factory functions or classes providing the
<a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> and <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> interface resp. Error handling
is done in the same way as defined for the stream readers and writers.</p>
</dd></dl>

<p><a class="reference internal" href="#codecs.StreamReaderWriter" title="codecs.StreamReaderWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReaderWriter</span></code></a> instances define the combined interfaces of
<a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> and <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> classes. They inherit all other
methods and attributes from the underlying stream.</p>
</div>
<div class="section" id="streamrecoder-objects">
<span id="stream-recoder-objects"></span><h4>StreamRecoder Objects<a class="headerlink" href="#streamrecoder-objects" title="永久链接至标题">¶</a></h4>
<p>The <a class="reference internal" href="#codecs.StreamRecoder" title="codecs.StreamRecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamRecoder</span></code></a> translates data from one encoding to another,
which is sometimes useful when dealing with different encoding environments.</p>
<p>The design is such that one can use the factory functions returned by the
<a class="reference internal" href="#codecs.lookup" title="codecs.lookup"><code class="xref py py-func docutils literal notranslate"><span class="pre">lookup()</span></code></a> function to construct the instance.</p>
<dl class="class">
<dt id="codecs.StreamRecoder">
<em class="property">class </em><code class="descclassname">codecs.</code><code class="descname">StreamRecoder</code><span class="sig-paren">(</span><em>stream</em>, <em>encode</em>, <em>decode</em>, <em>Reader</em>, <em>Writer</em>, <em>errors='strict'</em><span class="sig-paren">)</span><a class="headerlink" href="#codecs.StreamRecoder" title="永久链接至目标">¶</a></dt>
<dd><p>Creates a <a class="reference internal" href="#codecs.StreamRecoder" title="codecs.StreamRecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamRecoder</span></code></a> instance which implements a two-way conversion:
<em>encode</em> and <em>decode</em> work on the frontend&nbsp;— the data visible to
code calling <code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">write()</span></code>, while <em>Reader</em> and <em>Writer</em>
work on the backend&nbsp;— the data in <em>stream</em>.</p>
<p>You can use these objects to do transparent transcodings from e.g. Latin-1
to UTF-8 and back.</p>
<p>The <em>stream</em> argument must be a file-like object.</p>
<p>The <em>encode</em> and <em>decode</em> arguments must
adhere to the <code class="xref py py-class docutils literal notranslate"><span class="pre">Codec</span></code> interface. <em>Reader</em> and
<em>Writer</em> must be factory functions or classes providing objects of the
<a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> and <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> interface respectively.</p>
<p>Error handling is done in the same way as defined for the stream readers and
writers.</p>
</dd></dl>

<p><a class="reference internal" href="#codecs.StreamRecoder" title="codecs.StreamRecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamRecoder</span></code></a> instances define the combined interfaces of
<a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> and <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> classes. They inherit all other
methods and attributes from the underlying stream.</p>
</div>
</div>
</div>
<div class="section" id="encodings-and-unicode">
<span id="encodings-overview"></span><h2>Encodings and Unicode<a class="headerlink" href="#encodings-and-unicode" title="永久链接至标题">¶</a></h2>
<p>Strings are stored internally as sequences of code points in
range <code class="docutils literal notranslate"><span class="pre">0x0</span></code>--<code class="docutils literal notranslate"><span class="pre">0x10FFFF</span></code>.  (See <span class="target" id="index-3"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0393"><strong>PEP 393</strong></a> for
more details about the implementation.)
Once a string object is used outside of CPU and memory, endianness
and how these arrays are stored as bytes become an issue.  As with other
codecs, serialising a string into a sequence of bytes is known as <em>encoding</em>,
and recreating the string from the sequence of bytes is known as <em>decoding</em>.
There are a variety of different text serialisation codecs, which are
collectivity referred to as <a class="reference internal" href="../glossary.html#term-text-encoding"><span class="xref std std-term">text encodings</span></a>.</p>
<p>The simplest text encoding (called <code class="docutils literal notranslate"><span class="pre">'latin-1'</span></code> or <code class="docutils literal notranslate"><span class="pre">'iso-8859-1'</span></code>) maps
the code points 0--255 to the bytes <code class="docutils literal notranslate"><span class="pre">0x0</span></code>--<code class="docutils literal notranslate"><span class="pre">0xff</span></code>, which means that a string
object that contains code points above <code class="docutils literal notranslate"><span class="pre">U+00FF</span></code> can't be encoded with this
codec. Doing so will raise a <a class="reference internal" href="exceptions.html#UnicodeEncodeError" title="UnicodeEncodeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnicodeEncodeError</span></code></a> that looks
like the following (although the details of the error message may differ):
<code class="docutils literal notranslate"><span class="pre">UnicodeEncodeError:</span> <span class="pre">'latin-1'</span> <span class="pre">codec</span> <span class="pre">can't</span> <span class="pre">encode</span> <span class="pre">character</span> <span class="pre">'\u1234'</span> <span class="pre">in</span>
<span class="pre">position</span> <span class="pre">3:</span> <span class="pre">ordinal</span> <span class="pre">not</span> <span class="pre">in</span> <span class="pre">range(256)</span></code>.</p>
<p>There's another group of encodings (the so called charmap encodings) that choose
a different subset of all Unicode code points and how these code points are
mapped to the bytes <code class="docutils literal notranslate"><span class="pre">0x0</span></code>--<code class="docutils literal notranslate"><span class="pre">0xff</span></code>. To see how this is done simply open
e.g. <code class="file docutils literal notranslate"><span class="pre">encodings/cp1252.py</span></code> (which is an encoding that is used primarily on
Windows). There's a string constant with 256 characters that shows you which
character is mapped to which byte value.</p>
<p>All of these encodings can only encode 256 of the 1114112 code points
defined in Unicode. A simple and straightforward way that can store each Unicode
code point, is to store each code point as four consecutive bytes. There are two
possibilities: store the bytes in big endian or in little endian order. These
two encodings are called <code class="docutils literal notranslate"><span class="pre">UTF-32-BE</span></code> and <code class="docutils literal notranslate"><span class="pre">UTF-32-LE</span></code> respectively. Their
disadvantage is that if e.g. you use <code class="docutils literal notranslate"><span class="pre">UTF-32-BE</span></code> on a little endian machine you
will always have to swap bytes on encoding and decoding. <code class="docutils literal notranslate"><span class="pre">UTF-32</span></code> avoids this
problem: bytes will always be in natural endianness. When these bytes are read
by a CPU with a different endianness, then bytes have to be swapped though. To
be able to detect the endianness of a <code class="docutils literal notranslate"><span class="pre">UTF-16</span></code> or <code class="docutils literal notranslate"><span class="pre">UTF-32</span></code> byte sequence,
there's the so called BOM (&quot;Byte Order Mark&quot;). This is the Unicode character
<code class="docutils literal notranslate"><span class="pre">U+FEFF</span></code>. This character can be prepended to every <code class="docutils literal notranslate"><span class="pre">UTF-16</span></code> or <code class="docutils literal notranslate"><span class="pre">UTF-32</span></code>
byte sequence. The byte swapped version of this character (<code class="docutils literal notranslate"><span class="pre">0xFFFE</span></code>) is an
illegal character that may not appear in a Unicode text. So when the
first character in an <code class="docutils literal notranslate"><span class="pre">UTF-16</span></code> or <code class="docutils literal notranslate"><span class="pre">UTF-32</span></code> byte sequence
appears to be a <code class="docutils literal notranslate"><span class="pre">U+FFFE</span></code> the bytes have to be swapped on decoding.
Unfortunately the character <code class="docutils literal notranslate"><span class="pre">U+FEFF</span></code> had a second purpose as
a <code class="docutils literal notranslate"><span class="pre">ZERO</span> <span class="pre">WIDTH</span> <span class="pre">NO-BREAK</span> <span class="pre">SPACE</span></code>: a character that has no width and doesn't allow
a word to be split. It can e.g. be used to give hints to a ligature algorithm.
With Unicode 4.0 using <code class="docutils literal notranslate"><span class="pre">U+FEFF</span></code> as a <code class="docutils literal notranslate"><span class="pre">ZERO</span> <span class="pre">WIDTH</span> <span class="pre">NO-BREAK</span> <span class="pre">SPACE</span></code> has been
deprecated (with <code class="docutils literal notranslate"><span class="pre">U+2060</span></code> (<code class="docutils literal notranslate"><span class="pre">WORD</span> <span class="pre">JOINER</span></code>) assuming this role). Nevertheless
Unicode software still must be able to handle <code class="docutils literal notranslate"><span class="pre">U+FEFF</span></code> in both roles: as a BOM
it's a device to determine the storage layout of the encoded bytes, and vanishes
once the byte sequence has been decoded into a string; as a <code class="docutils literal notranslate"><span class="pre">ZERO</span> <span class="pre">WIDTH</span>
<span class="pre">NO-BREAK</span> <span class="pre">SPACE</span></code> it's a normal character that will be decoded like any other.</p>
<p>There's another encoding that is able to encoding the full range of Unicode
characters: UTF-8. UTF-8 is an 8-bit encoding, which means there are no issues
with byte order in UTF-8. Each byte in a UTF-8 byte sequence consists of two
parts: marker bits (the most significant bits) and payload bits. The marker bits
are a sequence of zero to four <code class="docutils literal notranslate"><span class="pre">1</span></code> bits followed by a <code class="docutils literal notranslate"><span class="pre">0</span></code> bit. Unicode characters are
encoded like this (with x being payload bits, which when concatenated give the
Unicode character):</p>
<table border="1" class="docutils">
<colgroup>
<col width="43%" />
<col width="57%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Range</th>
<th class="head">Encoding</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">U-00000000</span></code> ... <code class="docutils literal notranslate"><span class="pre">U-0000007F</span></code></td>
<td>0xxxxxxx</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">U-00000080</span></code> ... <code class="docutils literal notranslate"><span class="pre">U-000007FF</span></code></td>
<td>110xxxxx 10xxxxxx</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">U-00000800</span></code> ... <code class="docutils literal notranslate"><span class="pre">U-0000FFFF</span></code></td>
<td>1110xxxx 10xxxxxx 10xxxxxx</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">U-00010000</span></code> ... <code class="docutils literal notranslate"><span class="pre">U-0010FFFF</span></code></td>
<td>11110xxx 10xxxxxx 10xxxxxx 10xxxxxx</td>
</tr>
</tbody>
</table>
<p>The least significant bit of the Unicode character is the rightmost x bit.</p>
<p>As UTF-8 is an 8-bit encoding no BOM is required and any <code class="docutils literal notranslate"><span class="pre">U+FEFF</span></code> character in
the decoded string (even if it's the first character) is treated as a <code class="docutils literal notranslate"><span class="pre">ZERO</span>
<span class="pre">WIDTH</span> <span class="pre">NO-BREAK</span> <span class="pre">SPACE</span></code>.</p>
<p>Without external information it's impossible to reliably determine which
encoding was used for encoding a string. Each charmap encoding can
decode any random byte sequence. However that's not possible with UTF-8, as
UTF-8 byte sequences have a structure that doesn't allow arbitrary byte
sequences. To increase the reliability with which a UTF-8 encoding can be
detected, Microsoft invented a variant of UTF-8 (that Python 2.5 calls
<code class="docutils literal notranslate"><span class="pre">&quot;utf-8-sig&quot;</span></code>) for its Notepad program: Before any of the Unicode characters
is written to the file, a UTF-8 encoded BOM (which looks like this as a byte
sequence: <code class="docutils literal notranslate"><span class="pre">0xef</span></code>, <code class="docutils literal notranslate"><span class="pre">0xbb</span></code>, <code class="docutils literal notranslate"><span class="pre">0xbf</span></code>) is written. As it's rather improbable
that any charmap encoded file starts with these byte values (which would e.g.
map to</p>
<blockquote>
<div><div class="line-block">
<div class="line">LATIN SMALL LETTER I WITH DIAERESIS</div>
<div class="line">RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK</div>
<div class="line">INVERTED QUESTION MARK</div>
</div>
</div></blockquote>
<p>in iso-8859-1), this increases the probability that a <code class="docutils literal notranslate"><span class="pre">utf-8-sig</span></code> encoding can be
correctly guessed from the byte sequence. So here the BOM is not used to be able
to determine the byte order used for generating the byte sequence, but as a
signature that helps in guessing the encoding. On encoding the utf-8-sig codec
will write <code class="docutils literal notranslate"><span class="pre">0xef</span></code>, <code class="docutils literal notranslate"><span class="pre">0xbb</span></code>, <code class="docutils literal notranslate"><span class="pre">0xbf</span></code> as the first three bytes to the file. On
decoding <code class="docutils literal notranslate"><span class="pre">utf-8-sig</span></code> will skip those three bytes if they appear as the first
three bytes in the file.  In UTF-8, the use of the BOM is discouraged and
should generally be avoided.</p>
</div>
<div class="section" id="standard-encodings">
<span id="id3"></span><h2>Standard Encodings<a class="headerlink" href="#standard-encodings" title="永久链接至标题">¶</a></h2>
<p>Python comes with a number of codecs built-in, either implemented as C functions
or with dictionaries as mapping tables. The following table lists the codecs by
name, together with a few common aliases, and the languages for which the
encoding is likely used. Neither the list of aliases nor the list of languages
is meant to be exhaustive. Notice that spelling alternatives that only differ in
case or use a hyphen instead of an underscore are also valid aliases; therefore,
e.g. <code class="docutils literal notranslate"><span class="pre">'utf-8'</span></code> is a valid alias for the <code class="docutils literal notranslate"><span class="pre">'utf_8'</span></code> codec.</p>
<div class="impl-detail compound">
<p class="compound-first"><strong>CPython implementation detail:</strong> Some common encodings can bypass the codecs lookup machinery to
improve performance.  These optimization opportunities are only
recognized by CPython for a limited set of (case insensitive)
aliases: utf-8, utf8, latin-1, latin1, iso-8859-1, iso8859-1, mbcs
(Windows only), ascii, us-ascii, utf-16, utf16, utf-32, utf32, and
the same using underscores instead of dashes. Using alternative
aliases for these encodings may result in slower execution.</p>
<div class="compound-last versionchanged">
<p><span class="versionmodified">在 3.6 版更改: </span>Optimization opportunity recognized for us-ascii.</p>
</div>
</div>
<p>Many of the character sets support the same languages. They vary in individual
characters (e.g. whether the EURO SIGN is supported or not), and in the
assignment of characters to code positions. For the European languages in
particular, the following variants typically exist:</p>
<ul class="simple">
<li>an ISO 8859 codeset</li>
<li>a Microsoft Windows code page, which is typically derived from an 8859 codeset,
but replaces control characters with additional graphic characters</li>
<li>an IBM EBCDIC code page</li>
<li>an IBM PC code page, which is ASCII compatible</li>
</ul>
<table border="1" class="docutils">
<colgroup>
<col width="21%" />
<col width="40%" />
<col width="40%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Codec</th>
<th class="head">Aliases</th>
<th class="head">Languages</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>ascii</td>
<td>646, us-ascii</td>
<td>English</td>
</tr>
<tr class="row-odd"><td>big5</td>
<td>big5-tw, csbig5</td>
<td>Traditional Chinese</td>
</tr>
<tr class="row-even"><td>big5hkscs</td>
<td>big5-hkscs, hkscs</td>
<td>Traditional Chinese</td>
</tr>
<tr class="row-odd"><td>cp037</td>
<td>IBM037, IBM039</td>
<td>English</td>
</tr>
<tr class="row-even"><td>cp273</td>
<td>273, IBM273, csIBM273</td>
<td><p class="first">German</p>
<div class="last versionadded">
<p><span class="versionmodified">3.4 新版功能.</span></p>
</div>
</td>
</tr>
<tr class="row-odd"><td>cp424</td>
<td>EBCDIC-CP-HE, IBM424</td>
<td>Hebrew</td>
</tr>
<tr class="row-even"><td>cp437</td>
<td>437, IBM437</td>
<td>English</td>
</tr>
<tr class="row-odd"><td>cp500</td>
<td>EBCDIC-CP-BE, EBCDIC-CP-CH,
IBM500</td>
<td>Western Europe</td>
</tr>
<tr class="row-even"><td>cp720</td>
<td>&#160;</td>
<td>Arabic</td>
</tr>
<tr class="row-odd"><td>cp737</td>
<td>&#160;</td>
<td>Greek</td>
</tr>
<tr class="row-even"><td>cp775</td>
<td>IBM775</td>
<td>Baltic languages</td>
</tr>
<tr class="row-odd"><td>cp850</td>
<td>850, IBM850</td>
<td>Western Europe</td>
</tr>
<tr class="row-even"><td>cp852</td>
<td>852, IBM852</td>
<td>Central and Eastern Europe</td>
</tr>
<tr class="row-odd"><td>cp855</td>
<td>855, IBM855</td>
<td>Bulgarian, Byelorussian,
Macedonian, Russian, Serbian</td>
</tr>
<tr class="row-even"><td>cp856</td>
<td>&#160;</td>
<td>Hebrew</td>
</tr>
<tr class="row-odd"><td>cp857</td>
<td>857, IBM857</td>
<td>Turkish</td>
</tr>
<tr class="row-even"><td>cp858</td>
<td>858, IBM858</td>
<td>Western Europe</td>
</tr>
<tr class="row-odd"><td>cp860</td>
<td>860, IBM860</td>
<td>Portuguese</td>
</tr>
<tr class="row-even"><td>cp861</td>
<td>861, CP-IS, IBM861</td>
<td>Icelandic</td>
</tr>
<tr class="row-odd"><td>cp862</td>
<td>862, IBM862</td>
<td>Hebrew</td>
</tr>
<tr class="row-even"><td>cp863</td>
<td>863, IBM863</td>
<td>Canadian</td>
</tr>
<tr class="row-odd"><td>cp864</td>
<td>IBM864</td>
<td>Arabic</td>
</tr>
<tr class="row-even"><td>cp865</td>
<td>865, IBM865</td>
<td>Danish, Norwegian</td>
</tr>
<tr class="row-odd"><td>cp866</td>
<td>866, IBM866</td>
<td>Russian</td>
</tr>
<tr class="row-even"><td>cp869</td>
<td>869, CP-GR, IBM869</td>
<td>Greek</td>
</tr>
<tr class="row-odd"><td>cp874</td>
<td>&#160;</td>
<td>Thai</td>
</tr>
<tr class="row-even"><td>cp875</td>
<td>&#160;</td>
<td>Greek</td>
</tr>
<tr class="row-odd"><td>cp932</td>
<td>932, ms932, mskanji, ms-kanji</td>
<td>Japanese</td>
</tr>
<tr class="row-even"><td>cp949</td>
<td>949, ms949, uhc</td>
<td>Korean</td>
</tr>
<tr class="row-odd"><td>cp950</td>
<td>950, ms950</td>
<td>Traditional Chinese</td>
</tr>
<tr class="row-even"><td>cp1006</td>
<td>&#160;</td>
<td>Urdu</td>
</tr>
<tr class="row-odd"><td>cp1026</td>
<td>ibm1026</td>
<td>Turkish</td>
</tr>
<tr class="row-even"><td>cp1125</td>
<td>1125, ibm1125, cp866u, ruscii</td>
<td><p class="first">Ukrainian</p>
<div class="last versionadded">
<p><span class="versionmodified">3.4 新版功能.</span></p>
</div>
</td>
</tr>
<tr class="row-odd"><td>cp1140</td>
<td>ibm1140</td>
<td>Western Europe</td>
</tr>
<tr class="row-even"><td>cp1250</td>
<td>windows-1250</td>
<td>Central and Eastern Europe</td>
</tr>
<tr class="row-odd"><td>cp1251</td>
<td>windows-1251</td>
<td>Bulgarian, Byelorussian,
Macedonian, Russian, Serbian</td>
</tr>
<tr class="row-even"><td>cp1252</td>
<td>windows-1252</td>
<td>Western Europe</td>
</tr>
<tr class="row-odd"><td>cp1253</td>
<td>windows-1253</td>
<td>Greek</td>
</tr>
<tr class="row-even"><td>cp1254</td>
<td>windows-1254</td>
<td>Turkish</td>
</tr>
<tr class="row-odd"><td>cp1255</td>
<td>windows-1255</td>
<td>Hebrew</td>
</tr>
<tr class="row-even"><td>cp1256</td>
<td>windows-1256</td>
<td>Arabic</td>
</tr>
<tr class="row-odd"><td>cp1257</td>
<td>windows-1257</td>
<td>Baltic languages</td>
</tr>
<tr class="row-even"><td>cp1258</td>
<td>windows-1258</td>
<td>Vietnamese</td>
</tr>
<tr class="row-odd"><td>cp65001</td>
<td>&#160;</td>
<td><p class="first">Windows only: Windows UTF-8
(<code class="docutils literal notranslate"><span class="pre">CP_UTF8</span></code>)</p>
<div class="last versionadded">
<p><span class="versionmodified">3.3 新版功能.</span></p>
</div>
</td>
</tr>
<tr class="row-even"><td>euc_jp</td>
<td>eucjp, ujis, u-jis</td>
<td>Japanese</td>
</tr>
<tr class="row-odd"><td>euc_jis_2004</td>
<td>jisx0213, eucjis2004</td>
<td>Japanese</td>
</tr>
<tr class="row-even"><td>euc_jisx0213</td>
<td>eucjisx0213</td>
<td>Japanese</td>
</tr>
<tr class="row-odd"><td>euc_kr</td>
<td>euckr, korean, ksc5601,
ks_c-5601, ks_c-5601-1987,
ksx1001, ks_x-1001</td>
<td>Korean</td>
</tr>
<tr class="row-even"><td>gb2312</td>
<td>chinese, csiso58gb231280,
euc-cn, euccn, eucgb2312-cn,
gb2312-1980, gb2312-80,
iso-ir-58</td>
<td>Simplified Chinese</td>
</tr>
<tr class="row-odd"><td>gbk</td>
<td>936, cp936, ms936</td>
<td>Unified Chinese</td>
</tr>
<tr class="row-even"><td>gb18030</td>
<td>gb18030-2000</td>
<td>Unified Chinese</td>
</tr>
<tr class="row-odd"><td>hz</td>
<td>hzgb, hz-gb, hz-gb-2312</td>
<td>Simplified Chinese</td>
</tr>
<tr class="row-even"><td>iso2022_jp</td>
<td>csiso2022jp, iso2022jp,
iso-2022-jp</td>
<td>Japanese</td>
</tr>
<tr class="row-odd"><td>iso2022_jp_1</td>
<td>iso2022jp-1, iso-2022-jp-1</td>
<td>Japanese</td>
</tr>
<tr class="row-even"><td>iso2022_jp_2</td>
<td>iso2022jp-2, iso-2022-jp-2</td>
<td>Japanese, Korean, Simplified
Chinese, Western Europe, Greek</td>
</tr>
<tr class="row-odd"><td>iso2022_jp_2004</td>
<td>iso2022jp-2004,
iso-2022-jp-2004</td>
<td>Japanese</td>
</tr>
<tr class="row-even"><td>iso2022_jp_3</td>
<td>iso2022jp-3, iso-2022-jp-3</td>
<td>Japanese</td>
</tr>
<tr class="row-odd"><td>iso2022_jp_ext</td>
<td>iso2022jp-ext, iso-2022-jp-ext</td>
<td>Japanese</td>
</tr>
<tr class="row-even"><td>iso2022_kr</td>
<td>csiso2022kr, iso2022kr,
iso-2022-kr</td>
<td>Korean</td>
</tr>
<tr class="row-odd"><td>latin_1</td>
<td>iso-8859-1, iso8859-1, 8859,
cp819, latin, latin1, L1</td>
<td>West Europe</td>
</tr>
<tr class="row-even"><td>iso8859_2</td>
<td>iso-8859-2, latin2, L2</td>
<td>Central and Eastern Europe</td>
</tr>
<tr class="row-odd"><td>iso8859_3</td>
<td>iso-8859-3, latin3, L3</td>
<td>Esperanto, Maltese</td>
</tr>
<tr class="row-even"><td>iso8859_4</td>
<td>iso-8859-4, latin4, L4</td>
<td>Baltic languages</td>
</tr>
<tr class="row-odd"><td>iso8859_5</td>
<td>iso-8859-5, cyrillic</td>
<td>Bulgarian, Byelorussian,
Macedonian, Russian, Serbian</td>
</tr>
<tr class="row-even"><td>iso8859_6</td>
<td>iso-8859-6, arabic</td>
<td>Arabic</td>
</tr>
<tr class="row-odd"><td>iso8859_7</td>
<td>iso-8859-7, greek, greek8</td>
<td>Greek</td>
</tr>
<tr class="row-even"><td>iso8859_8</td>
<td>iso-8859-8, hebrew</td>
<td>Hebrew</td>
</tr>
<tr class="row-odd"><td>iso8859_9</td>
<td>iso-8859-9, latin5, L5</td>
<td>Turkish</td>
</tr>
<tr class="row-even"><td>iso8859_10</td>
<td>iso-8859-10, latin6, L6</td>
<td>Nordic languages</td>
</tr>
<tr class="row-odd"><td>iso8859_11</td>
<td>iso-8859-11, thai</td>
<td>Thai languages</td>
</tr>
<tr class="row-even"><td>iso8859_13</td>
<td>iso-8859-13, latin7, L7</td>
<td>Baltic languages</td>
</tr>
<tr class="row-odd"><td>iso8859_14</td>
<td>iso-8859-14, latin8, L8</td>
<td>Celtic languages</td>
</tr>
<tr class="row-even"><td>iso8859_15</td>
<td>iso-8859-15, latin9, L9</td>
<td>Western Europe</td>
</tr>
<tr class="row-odd"><td>iso8859_16</td>
<td>iso-8859-16, latin10, L10</td>
<td>South-Eastern Europe</td>
</tr>
<tr class="row-even"><td>johab</td>
<td>cp1361, ms1361</td>
<td>Korean</td>
</tr>
<tr class="row-odd"><td>koi8_r</td>
<td>&#160;</td>
<td>Russian</td>
</tr>
<tr class="row-even"><td>koi8_t</td>
<td>&#160;</td>
<td><p class="first">Tajik</p>
<div class="last versionadded">
<p><span class="versionmodified">3.5 新版功能.</span></p>
</div>
</td>
</tr>
<tr class="row-odd"><td>koi8_u</td>
<td>&#160;</td>
<td>Ukrainian</td>
</tr>
<tr class="row-even"><td>kz1048</td>
<td>kz_1048, strk1048_2002, rk1048</td>
<td><p class="first">Kazakh</p>
<div class="last versionadded">
<p><span class="versionmodified">3.5 新版功能.</span></p>
</div>
</td>
</tr>
<tr class="row-odd"><td>mac_cyrillic</td>
<td>maccyrillic</td>
<td>Bulgarian, Byelorussian,
Macedonian, Russian, Serbian</td>
</tr>
<tr class="row-even"><td>mac_greek</td>
<td>macgreek</td>
<td>Greek</td>
</tr>
<tr class="row-odd"><td>mac_iceland</td>
<td>maciceland</td>
<td>Icelandic</td>
</tr>
<tr class="row-even"><td>mac_latin2</td>
<td>maclatin2, maccentraleurope</td>
<td>Central and Eastern Europe</td>
</tr>
<tr class="row-odd"><td>mac_roman</td>
<td>macroman, macintosh</td>
<td>Western Europe</td>
</tr>
<tr class="row-even"><td>mac_turkish</td>
<td>macturkish</td>
<td>Turkish</td>
</tr>
<tr class="row-odd"><td>ptcp154</td>
<td>csptcp154, pt154, cp154,
cyrillic-asian</td>
<td>Kazakh</td>
</tr>
<tr class="row-even"><td>shift_jis</td>
<td>csshiftjis, shiftjis, sjis,
s_jis</td>
<td>Japanese</td>
</tr>
<tr class="row-odd"><td>shift_jis_2004</td>
<td>shiftjis2004, sjis_2004,
sjis2004</td>
<td>Japanese</td>
</tr>
<tr class="row-even"><td>shift_jisx0213</td>
<td>shiftjisx0213, sjisx0213,
s_jisx0213</td>
<td>Japanese</td>
</tr>
<tr class="row-odd"><td>utf_32</td>
<td>U32, utf32</td>
<td>all languages</td>
</tr>
<tr class="row-even"><td>utf_32_be</td>
<td>UTF-32BE</td>
<td>all languages</td>
</tr>
<tr class="row-odd"><td>utf_32_le</td>
<td>UTF-32LE</td>
<td>all languages</td>
</tr>
<tr class="row-even"><td>utf_16</td>
<td>U16, utf16</td>
<td>all languages</td>
</tr>
<tr class="row-odd"><td>utf_16_be</td>
<td>UTF-16BE</td>
<td>all languages</td>
</tr>
<tr class="row-even"><td>utf_16_le</td>
<td>UTF-16LE</td>
<td>all languages</td>
</tr>
<tr class="row-odd"><td>utf_7</td>
<td>U7, unicode-1-1-utf-7</td>
<td>all languages</td>
</tr>
<tr class="row-even"><td>utf_8</td>
<td>U8, UTF, utf8</td>
<td>all languages</td>
</tr>
<tr class="row-odd"><td>utf_8_sig</td>
<td>&#160;</td>
<td>all languages</td>
</tr>
</tbody>
</table>
<div class="versionchanged">
<p><span class="versionmodified">在 3.4 版更改: </span>The utf-16* and utf-32* encoders no longer allow surrogate code points
(<code class="docutils literal notranslate"><span class="pre">U+D800</span></code>--<code class="docutils literal notranslate"><span class="pre">U+DFFF</span></code>) to be encoded.
The utf-32* decoders no longer decode
byte sequences that correspond to surrogate code points.</p>
</div>
</div>
<div class="section" id="python-specific-encodings">
<h2>Python Specific Encodings<a class="headerlink" href="#python-specific-encodings" title="永久链接至标题">¶</a></h2>
<p>A number of predefined codecs are specific to Python, so their codec names have
no meaning outside Python.  These are listed in the tables below based on the
expected input and output types (note that while text encodings are the most
common use case for codecs, the underlying codec infrastructure supports
arbitrary data transforms rather than just text encodings).  For asymmetric
codecs, the stated purpose describes the encoding direction.</p>
<div class="section" id="text-encodings">
<h3>Text Encodings<a class="headerlink" href="#text-encodings" title="永久链接至标题">¶</a></h3>
<p>The following codecs provide <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> to <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> encoding and
<a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a> to <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> decoding, similar to the Unicode text
encodings.</p>
<table border="1" class="docutils">
<colgroup>
<col width="36%" />
<col width="16%" />
<col width="48%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Codec</th>
<th class="head">Aliases</th>
<th class="head">目的</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>idna</td>
<td>&#160;</td>
<td>Implements <span class="target" id="index-4"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc3490.html"><strong>RFC 3490</strong></a>,
see also
<a class="reference internal" href="#module-encodings.idna" title="encodings.idna: Internationalized Domain Names implementation"><code class="xref py py-mod docutils literal notranslate"><span class="pre">encodings.idna</span></code></a>.
Only <code class="docutils literal notranslate"><span class="pre">errors='strict'</span></code>
is supported.</td>
</tr>
<tr class="row-odd"><td>mbcs</td>
<td>ansi,
dbcs</td>
<td>Windows only: Encode
operand according to the
ANSI codepage (CP_ACP)</td>
</tr>
<tr class="row-even"><td>oem</td>
<td>&#160;</td>
<td><p class="first">Windows only: Encode
operand according to the
OEM codepage (CP_OEMCP)</p>
<div class="last versionadded">
<p><span class="versionmodified">3.6 新版功能.</span></p>
</div>
</td>
</tr>
<tr class="row-odd"><td>palmos</td>
<td>&#160;</td>
<td>Encoding of PalmOS 3.5</td>
</tr>
<tr class="row-even"><td>punycode</td>
<td>&#160;</td>
<td>Implements <span class="target" id="index-5"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc3492.html"><strong>RFC 3492</strong></a>.
Stateful codecs are not
supported.</td>
</tr>
<tr class="row-odd"><td>raw_unicode_escape</td>
<td>&#160;</td>
<td>Latin-1 encoding with
<code class="docutils literal notranslate"><span class="pre">\uXXXX</span></code> and
<code class="docutils literal notranslate"><span class="pre">\UXXXXXXXX</span></code> for other
code points. Existing
backslashes are not
escaped in any way.
It is used in the Python
pickle protocol.</td>
</tr>
<tr class="row-even"><td>undefined</td>
<td>&#160;</td>
<td>Raise an exception for
all conversions, even
empty strings. The error
handler is ignored.</td>
</tr>
<tr class="row-odd"><td>unicode_escape</td>
<td>&#160;</td>
<td>Encoding suitable as the
contents of a Unicode
literal in ASCII-encoded
Python source code,
except that quotes are
not escaped. Decodes from
Latin-1 source code.
Beware that Python source
code actually uses UTF-8
by default.</td>
</tr>
<tr class="row-even"><td>unicode_internal</td>
<td>&#160;</td>
<td><p class="first">Return the internal
representation of the
operand. Stateful codecs
are not supported.</p>
<div class="last deprecated">
<p><span class="versionmodified">3.3 版后已移除: </span>This representation is
obsoleted by
<span class="target" id="index-6"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0393"><strong>PEP 393</strong></a>.</p>
</div>
</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="binary-transforms">
<span id="id4"></span><h3>Binary Transforms<a class="headerlink" href="#binary-transforms" title="永久链接至标题">¶</a></h3>
<p>The following codecs provide binary transforms: <a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a>
to <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> mappings.  They are not supported by <a class="reference internal" href="stdtypes.html#bytes.decode" title="bytes.decode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">bytes.decode()</span></code></a>
(which only produces <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> output).</p>
<table border="1" class="docutils">
<colgroup>
<col width="22%" />
<col width="18%" />
<col width="30%" />
<col width="30%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Codec</th>
<th class="head">Aliases</th>
<th class="head">目的</th>
<th class="head">Encoder / decoder</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>base64_codec <a class="footnote-reference" href="#b64" id="id5">[1]</a></td>
<td>base64, base_64</td>
<td><p class="first">Convert operand to multiline
MIME base64 (the result
always includes a trailing
<code class="docutils literal notranslate"><span class="pre">'\n'</span></code>)</p>
<div class="last versionchanged">
<p><span class="versionmodified">在 3.4 版更改: </span>accepts any
<a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a>
as input for encoding and
decoding</p>
</div>
</td>
<td><a class="reference internal" href="base64.html#base64.encodebytes" title="base64.encodebytes"><code class="xref py py-meth docutils literal notranslate"><span class="pre">base64.encodebytes()</span></code></a> /
<a class="reference internal" href="base64.html#base64.decodebytes" title="base64.decodebytes"><code class="xref py py-meth docutils literal notranslate"><span class="pre">base64.decodebytes()</span></code></a></td>
</tr>
<tr class="row-odd"><td>bz2_codec</td>
<td>bz2</td>
<td>Compress the operand
using bz2</td>
<td><a class="reference internal" href="bz2.html#bz2.compress" title="bz2.compress"><code class="xref py py-meth docutils literal notranslate"><span class="pre">bz2.compress()</span></code></a> /
<a class="reference internal" href="bz2.html#bz2.decompress" title="bz2.decompress"><code class="xref py py-meth docutils literal notranslate"><span class="pre">bz2.decompress()</span></code></a></td>
</tr>
<tr class="row-even"><td>hex_codec</td>
<td>hex</td>
<td>Convert operand to
hexadecimal
representation, with two
digits per byte</td>
<td><a class="reference internal" href="binascii.html#binascii.b2a_hex" title="binascii.b2a_hex"><code class="xref py py-meth docutils literal notranslate"><span class="pre">binascii.b2a_hex()</span></code></a> /
<a class="reference internal" href="binascii.html#binascii.a2b_hex" title="binascii.a2b_hex"><code class="xref py py-meth docutils literal notranslate"><span class="pre">binascii.a2b_hex()</span></code></a></td>
</tr>
<tr class="row-odd"><td>quopri_codec</td>
<td>quopri,
quotedprintable,
quoted_printable</td>
<td>Convert operand to MIME
quoted printable</td>
<td><a class="reference internal" href="quopri.html#quopri.encode" title="quopri.encode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">quopri.encode()</span></code></a> with
<code class="docutils literal notranslate"><span class="pre">quotetabs=True</span></code> /
<a class="reference internal" href="quopri.html#quopri.decode" title="quopri.decode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">quopri.decode()</span></code></a></td>
</tr>
<tr class="row-even"><td>uu_codec</td>
<td>uu</td>
<td>Convert the operand using
uuencode</td>
<td><a class="reference internal" href="uu.html#uu.encode" title="uu.encode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">uu.encode()</span></code></a> /
<a class="reference internal" href="uu.html#uu.decode" title="uu.decode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">uu.decode()</span></code></a></td>
</tr>
<tr class="row-odd"><td>zlib_codec</td>
<td>zip, zlib</td>
<td>Compress the operand
using gzip</td>
<td><a class="reference internal" href="zlib.html#zlib.compress" title="zlib.compress"><code class="xref py py-meth docutils literal notranslate"><span class="pre">zlib.compress()</span></code></a> /
<a class="reference internal" href="zlib.html#zlib.decompress" title="zlib.decompress"><code class="xref py py-meth docutils literal notranslate"><span class="pre">zlib.decompress()</span></code></a></td>
</tr>
</tbody>
</table>
<table class="docutils footnote" frame="void" id="b64" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id5">[1]</a></td><td>In addition to <a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like objects</span></a>,
<code class="docutils literal notranslate"><span class="pre">'base64_codec'</span></code> also accepts ASCII-only instances of <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> for
decoding</td></tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">3.2 新版功能: </span>Restoration of the binary transforms.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">在 3.4 版更改: </span>Restoration of the aliases for the binary transforms.</p>
</div>
</div>
<div class="section" id="text-transforms">
<span id="id6"></span><h3>Text Transforms<a class="headerlink" href="#text-transforms" title="永久链接至标题">¶</a></h3>
<p>The following codec provides a text transform: a <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> to <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>
mapping.  It is not supported by <a class="reference internal" href="stdtypes.html#str.encode" title="str.encode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">str.encode()</span></code></a> (which only produces
<a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> output).</p>
<table border="1" class="docutils">
<colgroup>
<col width="36%" />
<col width="16%" />
<col width="48%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Codec</th>
<th class="head">Aliases</th>
<th class="head">目的</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>rot_13</td>
<td>rot13</td>
<td>Returns the Caesar-cypher
encryption of the operand</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">3.2 新版功能: </span>Restoration of the <code class="docutils literal notranslate"><span class="pre">rot_13</span></code> text transform.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">在 3.4 版更改: </span>Restoration of the <code class="docutils literal notranslate"><span class="pre">rot13</span></code> alias.</p>
</div>
</div>
</div>
<div class="section" id="module-encodings.idna">
<span id="encodings-idna-internationalized-domain-names-in-applications"></span><h2><a class="reference internal" href="#module-encodings.idna" title="encodings.idna: Internationalized Domain Names implementation"><code class="xref py py-mod docutils literal notranslate"><span class="pre">encodings.idna</span></code></a> --- Internationalized Domain Names in Applications<a class="headerlink" href="#module-encodings.idna" title="永久链接至标题">¶</a></h2>
<p>This module implements <span class="target" id="index-7"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc3490.html"><strong>RFC 3490</strong></a> (Internationalized Domain Names in
Applications) and <span class="target" id="index-8"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc3492.html"><strong>RFC 3492</strong></a> (Nameprep: A Stringprep Profile for
Internationalized Domain Names (IDN)). It builds upon the <code class="docutils literal notranslate"><span class="pre">punycode</span></code> encoding
and <a class="reference internal" href="stringprep.html#module-stringprep" title="stringprep: String preparation, as per RFC 3453"><code class="xref py py-mod docutils literal notranslate"><span class="pre">stringprep</span></code></a>.</p>
<p>These RFCs together define a protocol to support non-ASCII characters in domain
names. A domain name containing non-ASCII characters (such as
<code class="docutils literal notranslate"><span class="pre">www.Alliancefrançaise.nu</span></code>) is converted into an ASCII-compatible encoding
(ACE, such as <code class="docutils literal notranslate"><span class="pre">www.xn--alliancefranaise-npb.nu</span></code>). The ACE form of the domain
name is then used in all places where arbitrary characters are not allowed by
the protocol, such as DNS queries, HTTP <em class="mailheader">Host</em> fields, and so
on. This conversion is carried out in the application; if possible invisible to
the user: The application should transparently convert Unicode domain labels to
IDNA on the wire, and convert back ACE labels to Unicode before presenting them
to the user.</p>
<p>Python supports this conversion in several ways:  the <code class="docutils literal notranslate"><span class="pre">idna</span></code> codec performs
conversion between Unicode and ACE, separating an input string into labels
based on the separator characters defined in <span class="target" id="index-9"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc3490.html#section-3.1"><strong>section 3.1 of RFC 3490</strong></a>
and converting each label to ACE as required, and conversely separating an input
byte string into labels based on the <code class="docutils literal notranslate"><span class="pre">.</span></code> separator and converting any ACE
labels found into unicode.  Furthermore, the <a class="reference internal" href="socket.html#module-socket" title="socket: Low-level networking interface."><code class="xref py py-mod docutils literal notranslate"><span class="pre">socket</span></code></a> module
transparently converts Unicode host names to ACE, so that applications need not
be concerned about converting host names themselves when they pass them to the
socket module. On top of that, modules that have host names as function
parameters, such as <a class="reference internal" href="http.client.html#module-http.client" title="http.client: HTTP and HTTPS protocol client (requires sockets)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">http.client</span></code></a> and <a class="reference internal" href="ftplib.html#module-ftplib" title="ftplib: FTP protocol client (requires sockets)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">ftplib</span></code></a>, accept Unicode host
names (<a class="reference internal" href="http.client.html#module-http.client" title="http.client: HTTP and HTTPS protocol client (requires sockets)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">http.client</span></code></a> then also transparently sends an IDNA hostname in the
<em class="mailheader">Host</em> field if it sends that field at all).</p>
<p>When receiving host names from the wire (such as in reverse name lookup), no
automatic conversion to Unicode is performed: Applications wishing to present
such host names to the user should decode them to Unicode.</p>
<p>The module <a class="reference internal" href="#module-encodings.idna" title="encodings.idna: Internationalized Domain Names implementation"><code class="xref py py-mod docutils literal notranslate"><span class="pre">encodings.idna</span></code></a> also implements the nameprep procedure, which
performs certain normalizations on host names, to achieve case-insensitivity of
international domain names, and to unify similar characters. The nameprep
functions can be used directly if desired.</p>
<dl class="function">
<dt id="encodings.idna.nameprep">
<code class="descclassname">encodings.idna.</code><code class="descname">nameprep</code><span class="sig-paren">(</span><em>label</em><span class="sig-paren">)</span><a class="headerlink" href="#encodings.idna.nameprep" title="永久链接至目标">¶</a></dt>
<dd><p>Return the nameprepped version of <em>label</em>. The implementation currently assumes
query strings, so <code class="docutils literal notranslate"><span class="pre">AllowUnassigned</span></code> is true.</p>
</dd></dl>

<dl class="function">
<dt id="encodings.idna.ToASCII">
<code class="descclassname">encodings.idna.</code><code class="descname">ToASCII</code><span class="sig-paren">(</span><em>label</em><span class="sig-paren">)</span><a class="headerlink" href="#encodings.idna.ToASCII" title="永久链接至目标">¶</a></dt>
<dd><p>Convert a label to ASCII, as specified in <span class="target" id="index-10"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc3490.html"><strong>RFC 3490</strong></a>. <code class="docutils literal notranslate"><span class="pre">UseSTD3ASCIIRules</span></code> is
assumed to be false.</p>
</dd></dl>

<dl class="function">
<dt id="encodings.idna.ToUnicode">
<code class="descclassname">encodings.idna.</code><code class="descname">ToUnicode</code><span class="sig-paren">(</span><em>label</em><span class="sig-paren">)</span><a class="headerlink" href="#encodings.idna.ToUnicode" title="永久链接至目标">¶</a></dt>
<dd><p>Convert a label to Unicode, as specified in <span class="target" id="index-11"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc3490.html"><strong>RFC 3490</strong></a>.</p>
</dd></dl>

</div>
<div class="section" id="module-encodings.mbcs">
<span id="encodings-mbcs-windows-ansi-codepage"></span><h2><a class="reference internal" href="#module-encodings.mbcs" title="encodings.mbcs: Windows ANSI codepage"><code class="xref py py-mod docutils literal notranslate"><span class="pre">encodings.mbcs</span></code></a> --- Windows ANSI codepage<a class="headerlink" href="#module-encodings.mbcs" title="永久链接至标题">¶</a></h2>
<p>Encode operand according to the ANSI codepage (CP_ACP).</p>
<p class="availability"><a class="reference internal" href="intro.html#availability"><span class="std std-ref">Availability</span></a>: Windows only.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.3 版更改: </span>Support any error handler.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">在 3.2 版更改: </span>Before 3.2, the <em>errors</em> argument was ignored; <code class="docutils literal notranslate"><span class="pre">'replace'</span></code> was always used
to encode, and <code class="docutils literal notranslate"><span class="pre">'ignore'</span></code> to decode.</p>
</div>
</div>
<div class="section" id="module-encodings.utf_8_sig">
<span id="encodings-utf-8-sig-utf-8-codec-with-bom-signature"></span><h2><a class="reference internal" href="#module-encodings.utf_8_sig" title="encodings.utf_8_sig: UTF-8 codec with BOM signature"><code class="xref py py-mod docutils literal notranslate"><span class="pre">encodings.utf_8_sig</span></code></a> --- UTF-8 codec with BOM signature<a class="headerlink" href="#module-encodings.utf_8_sig" title="永久链接至标题">¶</a></h2>
<p>This module implements a variant of the UTF-8 codec: On encoding a UTF-8 encoded
BOM will be prepended to the UTF-8 encoded bytes. For the stateful encoder this
is only done once (on the first write to the byte stream).  For decoding an
optional UTF-8 encoded BOM at the start of the data will be skipped.</p>
</div>
</div>


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  <h3><a href="../contents.html">Table of Contents</a></h3>
  <ul>
<li><a class="reference internal" href="#"><code class="docutils literal notranslate"><span class="pre">codecs</span></code> --- Codec registry and base classes</a><ul>
<li><a class="reference internal" href="#codec-base-classes">Codec Base Classes</a><ul>
<li><a class="reference internal" href="#error-handlers">Error Handlers</a></li>
<li><a class="reference internal" href="#stateless-encoding-and-decoding">Stateless Encoding and Decoding</a></li>
<li><a class="reference internal" href="#incremental-encoding-and-decoding">Incremental Encoding and Decoding</a><ul>
<li><a class="reference internal" href="#incrementalencoder-objects">IncrementalEncoder Objects</a></li>
<li><a class="reference internal" href="#incrementaldecoder-objects">IncrementalDecoder Objects</a></li>
</ul>
</li>
<li><a class="reference internal" href="#stream-encoding-and-decoding">Stream Encoding and Decoding</a><ul>
<li><a class="reference internal" href="#streamwriter-objects">StreamWriter Objects</a></li>
<li><a class="reference internal" href="#streamreader-objects">StreamReader Objects</a></li>
<li><a class="reference internal" href="#streamreaderwriter-objects">StreamReaderWriter Objects</a></li>
<li><a class="reference internal" href="#streamrecoder-objects">StreamRecoder Objects</a></li>
</ul>
</li>
</ul>
</li>
<li><a class="reference internal" href="#encodings-and-unicode">Encodings and Unicode</a></li>
<li><a class="reference internal" href="#standard-encodings">Standard Encodings</a></li>
<li><a class="reference internal" href="#python-specific-encodings">Python Specific Encodings</a><ul>
<li><a class="reference internal" href="#text-encodings">Text Encodings</a></li>
<li><a class="reference internal" href="#binary-transforms">Binary Transforms</a></li>
<li><a class="reference internal" href="#text-transforms">Text Transforms</a></li>
</ul>
</li>
<li><a class="reference internal" href="#module-encodings.idna"><code class="docutils literal notranslate"><span class="pre">encodings.idna</span></code> --- Internationalized Domain Names in Applications</a></li>
<li><a class="reference internal" href="#module-encodings.mbcs"><code class="docutils literal notranslate"><span class="pre">encodings.mbcs</span></code> --- Windows ANSI codepage</a></li>
<li><a class="reference internal" href="#module-encodings.utf_8_sig"><code class="docutils literal notranslate"><span class="pre">encodings.utf_8_sig</span></code> --- UTF-8 codec with BOM signature</a></li>
</ul>
</li>
</ul>

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